The use of micro-fabrication methods that self-assemble materials from individual particles, as in many naturally occurring processes, has grown over the past decade because of their ability to create intricate microstructures. One such method for forming monolayers of particles is the capillarity based self-assembly. In recent years, many studies have been conducted to understand this process because of the importance of monolayers in a range of technological applications, e.g., for forming novel micron and nano structured materials and for stabilizing emulsions, and also because the behavior of particles trapped on fluid interfaces is important for understanding a range of physical processes, e.g., the formation of pollen rafts which play an important role in hydrophilous pollination and the clustering of insect eggs.
A common example of capillarity-driven self-assembly is the clustering of breakfast-cereal flakes floating on the surface of milk. The deformation of the interface by the flakes gives rise to lateral capillary forces which cause them to cluster. This technique has been widely used for two-dimensional assembly of particles at liquid surfaces. It, however, produces monolayers which lack long range order and have defects, and the distance between the particles cannot be controlled as they touch each other. Furthermore, the technique cannot be used when lateral capillary forces arising because of the buoyant weight of particles, which vary as the sixed power of the radius, become smaller than Brownian forces. For particles floating on an air-water interface this limit is reached when the particle size is smaller than ˜10 μm. Particles smaller than this limiting size move randomly and do not cluster.